Author(s)

M. V. Nicolova, I. I. Spasova & S. N. Groudev

Abstract

The uranium deposit Curilo located in Western Bulgaria is an intensive source of acid drainage waters. These waters have a pH in the range of about 2.5–4 and contain radionuclides (uranium, radium), heavy metals (mainly iron, manganese, copper, zinc, cadmium), arsenic and sulphates in concentrations usually much higher than the relevant permissible levels for waters intended for use in agriculture and/or industry. The generation of acid waters is connected with the activity of the indigenous acidophilic chemolithotrophic bacteria, which oxidize the pyrite and other sulphide minerals present in the deposits. In 2000–2003 experiments were carried out to inhibit these bacteria in order to prevent the generation of acid drainage in a dump consisting of rich-in-pyrite mining waters. The inhibition was efficiently achieved by suitable changes in the levels of some essential environmental factors (the pH and the content of molecular oxygen and biodegradable organic substrates) in the dump which created conditions not favorable for the growth and activity of the acidophilic chemolithotrophs. Keywords: acid mine drainage, acidophilic chemolithotrophs, sulphate-reducing bacteria, water-saturated organic cover, dump recultivation. 1 Introduction The uranium deposit Curilo, located in Western Bulgaria, for a long period of time was a site of intensive mining activities including both the open-pit and underground mining techniques as well as the in situ leaching of uranium. The mining operations were ended in 1990 but since that time the deposit is a permanent source of acid drainage waters. These waters have pH in the range of about 2–4 and contain radionuclides (mainly uranium and radium), several heavy

Keywords

acid mine drainage, acidophilic chemolithotrophs, sulphate-reducing bacteria, water-saturated organic cover, dump recultivation.